1. Technical Field
The present invention relates to, for example, a MEMS (Micro Electro Mechanical Systems) device in which a functional element, such as a resonator, a sensor and an actuator, and/or an electronic circuit are integrated on one substrate, and a method of manufacturing such a MEMS device.
2. Related Art
For example, in a MEMS device that includes a resonator with capacitance as a functional element, the resonator is airtightly sealed, in a vacuum state, in a cavity formed in a substrate. Therefore, a cavity is formed by providing the substrate with a structural member that surrounds the resonator, and a lid portion (cap layer) is joined to the cavity with the inside of the cavity placed in a vacuum state.
Traditionally, an insulating substance of silicon nitride (P—SiN) and the like deposited using a plasma CVD (Chemical Vapor Deposition) technique is used as the lid portion for the cavity. However, in a case where the insulating substance of silicon nitride and the like is used as the lid portion for the cavity, high-vacuum cavity sealing required in a high-performance MEMS device cannot be realized.
Also, aluminum (Al), which is a material of wiring connected to impurity diffusion regions of a MOS field-effect transistor and the like, doubles as a material of a conductive member electrically connected to an external connection electrode of a functional element. However, in the case of a high-performance MOS field-effect transistor, a contact plug of tungsten (W) is used as a connecting member instead of the wiring of aluminum (Al). Therefore, a material of the connecting member for the functional element cannot double as a material of the connecting member for the high-performance MOS field-effect transistor.
As related art, the specification of U.S. Pat. No. 5,798,283 (columns 7 and 8, FIGS. 8 and 9) discloses MEM devices with an electronic circuitry on a common substrate. A cavity is formed in a substrate of these MEM devices, and silicon nitride (SiN) or silicon dioxide (SiO2) is used as a material of a lid portion (cap layer) for the cavity.
On the other hand, JP-A-2009-272477 (paragraphs 0020 to 0027, FIG. 1) discloses a MEMS sensor in which a cavity is formed by a structural member provided on a semiconductor substrate. In this MEMS sensor, a wall portion of the cavity is provided on a silicon substrate via an insulating layer of silicon oxide and the like, and a peripheral portion of a lid portion (cap) for the cavity is supported on the wall portion of the cavity via the insulating layer of silicon oxide and the like. Here, the cap, a ground conductive portion, and a voltage application conductive portion are made of doped polysilicon and are formed on the same layer.
The specification of U.S. Pat. No. 5,798,283 (columns 7 and 8, FIGS. 8 and 9) and JP-A-2009-272477 (paragraphs 0020 to 0027, FIG. 1) are examples of related art.
According to the specification of U.S. Pat. No. 5,798,283 (columns 7 and 8, FIGS. 8 and 9), as silicon nitride (SiN) or silicon dioxide (SiO2) is used as a material of the lid portion for the cavity, it is difficult to realize high-vacuum cavity sealing. On the other hand, in JP-A-2009-272477 (paragraphs 0020 to 0027, FIG. 1) that uses polysilicon with electrical conductivity as a material of the lid portion for the cavity, it is necessary to positionally align and join a side wall of the cavity and the lid portion with/to each other in a vacuum chamber. In addition, a structure for insulating and isolating a wiring portion for a functional element and the lid portion for the cavity from each other is important.